Three point hitch draft sensing system

ABSTRACT

A draft sensing mechanism for a three point hitch includes a hitch frame attached to a frame of a vehicle. The hitch frame includes left and right link supports for coupling to left and right draft links and left and right draft bars. Each draft bar has a first portion attached to a corresponding one of the link supports, and a second portion positioned rearwardly and inwardly with respect to its first portion. Draft forces applied by the draft links to the link supports are transmitted to the second portions of the draft bars. A linkage unit sums the draft forces from the draft bars and includes a draft force transducer which generates a draft force signal in response to deflection of the draft bars.

FIELD

The present disclosure relates to a draft force sensing system.

BACKGROUND

Agricultural implements can be mounted directly to agricultural tractorsusing a conventional three point hitch. Three point hitches have beencontrolled by a hitch control system which raises and lowers the hitchin response to a number of sensed parameters, including sensed draftforce. Such systems can operate to lower and raise an implement whilemaintaining a constant load on the tractor. The implement is actuallyable to work at a deeper average depth as the tractor is able to operateat a higher average power with this control system. Various draft forcesensing systems have been developed to provide a sensed draft forcesignal. Certain current production draft force sensing systems have anumber of moving parts that require periodical maintenance, includingremoving mud and dirt accumulation and lubrication of a draft sensorplunger to prevent moisture and dirt contamination. In certainconditions, the dirt and mud accumulation actually prevents componentmovement which causes false draft sensing signals. Changes in tractorframe design will require new draft force sensing designs.

Some production systems have costly draft sensing pins, bending bars,and draft sensing shafts. Draft sensing pins require two instrument pinswhich double the cost and halve the reliability. The bending bar anddraft sensing shaft systems have moving parts and require a sealedcompartment and a fair amount of space. The zero load voltage for thesystem is set by adjusting the length of a spring steel strap thatmounts over the sensor plunger and the ends of which are attached to thebody of the shaft. The factory consistently has issues setting thevoltage. The spring steel strap and sensor plunger produce aninconsistent voltage during spring steel strap adjustment. The currentdraft sensing system on 4WD tractors measures the deflection between thedraft link mount straps. The components are open to the elements andexposed to mud, dirt, and debris.

It is desired to provide a draft force sensing system which can beinstalled within the space available in future production tractors. Itis also desired to provide a draft force sensing system which is betterprotected from environmental contamination. It is desired to have asystem which is sealed and less prone to accumulate debris.

SUMMARY

According to an aspect of the present disclosure, a vehicle includesleft and right draft links for coupling an implement to a hitch frame. Adraft force sensing system includes a pair of L-bars coupled between thedraft links and a sensing unit. The sensing unit includes a housing andfirst and second spaced apart pivot pins mounted in the housing. A firstarm is pivotally mounted on the first pivot pin. The first arm has anfirst portion movable by one of the L-bars in response to draft forceapplied to the left draft link and has a second portion. A second arm ispivotally mounted on the second pivot pin. The second arm has an firstportion movable by the other L-bar in response to draft force applied tothe right draft link and has a second portion. A resilient member iscoupled to the first and second arms and is biased to urge the armstowards each other. A stop member is positioned between the arms and isengagable with the arms to limit movement of the arms towards eachother. A transducer engages the second portions of the first and secondarms. The transducer generates an electrical signal representing adistance between the second portions.

This draft force sensing system mechanically sums the horizontal draftload between the two lower draft links of a three point hitch. The twolower draft links are coupled to parts of a hitch frame which areflexible in response to horizontal loads and is stiff in response tovertical loads. The hitch frame structure and L-bar placement maximizesthe horizontal draft signal and minimizes vertical load signal. Thedraft sensing system requires very little space and does not requireperiodical lubrication and maintenance. The hitch frame is a castingwhich deflects in response to draft load. This deflection is transferredto the two L-bars mounted on the hitch frame. The L-bars have ends whichswing due to deflection and twisting of the hitch frame. The L-bar endspush against two round headed bolts which are connected to a linkageassembly in the sensing unit. The linkage assembly includes pivotingarms which magnify the deflection. The transducer is mounted between thearms, and is compressed or decompressed depending upon the draft loadapplied to the hitch frame. This system mechanically sums the draft loadfrom both lower draft link together, so that only a single transducer isrequired, thus increasing system reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective rear view of a tractor hitch frame and a threepoint hitch;

FIG. 2 is a perspective bottom front view of a tractor hitch frame and adraft sensing mechanism embodying the invention;

FIG. 2A is a perspective bottom front view of a tractor hitch frame withthe draft sensing mechanism removed;

FIG. 3 is a bottom view of the structure shown in FIG. 1;

FIG. 4 is a bottom perspective view of a portion of FIG. 4;

FIG. 5 is a sectional view along lines 5-5 of FIG. 4;

FIG. 6 is perspective view of a portion of the components shown in FIG.3, but with the drawbar and a housing cover removed for clarity;

FIG. 7 is a sectional view along lines 7-7 of FIG. 6; and

FIG. 8 is a sectional view along lines 8-8 of FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1, 2 and 3, a hitch frame 10 is adapted to beattached to a rear end frame of a work vehicle, such as an agriculturaltractor (not shown). The hitch frame 10 includes a main body 11 and leftand right draft link supports or draft ears 12 and 14. A conventionalthree point hitch 20 is mounted to the hitch frame 10, and includes leftand right draft links 24 and 26 which are coupled to the draft ears 12and 14 in a known manner. A conventional drawbar 28 extends in afore-and-aft direction below the hitch frame 10.

Referring now to FIG. 2A, each draft ear 12 and 14 of the hitch frame 10includes a corresponding forwardly facing mounting surface 13 and 15.The Hitch frame 10 forms a downwardly opening pocket 17 which extendsrearwardly with respect to the draft ears 12 and 13. Referring now toFIGS. 2-4, a draft sensing mechanism 30 senses draft forces which areapplied to the draft links 24 and 26, and generates an electrical draftforce signal. Mechanism 30 includes left and right L-shaped draft bars32 and 34. Each draft bar 32, 34 includes a first or forward part 36, 38which is attached to the mounting surface 13, 15 of a corresponding oneof the link supports 12, 14. Each draft bar 32, 34 also has a secondpart 44, 46 positioned rearwardly and inwardly with respect to thecorresponding first part 36, 38. The first parts 36, 38 projectlaterally outwardly and away from each other. Each second part 44, 46extends rearwardly from an inner end of the corresponding first part,36, 38. Each first part 36, 38 is joined to the second part 44, 46 by acorresponding curved joint 48, 50.

Referring now to FIGS. 3-5, a sensing unit or linkage unit 52 is mountedin the pocket 17 and is attached to a downwardly facing surface 54 ofthe hitch frame 10 between the draft bars 32 and 34 and between thedrawbar 28 and the hitch frame 10.

Referring now to FIG. 6, the sensing unit 52 includes a housing 56 whichforms a cavity 58. Cavity is surrounded by a seal groove 60 whichreceives a seal 62. The housing forms a left side wall 64 and a rightside wall 66. A left recess 68 is formed in the left side wall 64, and aright recess 70 is formed in the right side wall 66. Both recess 68 and70 are near but spaced apart from a rear end of the housing 56. A leftbore 74 communicates the cavity 58 with the left recess 68, and a rightbore 76 communicates the cavity 58 with the right recess 70. A harnessbore 78 communicates the cavity 58 with a harness recess 80 which isformed in the left side wall 64 near a forward end of the housing 56.Recess 80 is covered by a harness shield 82.

Referring now to FIGS. 6, 7 and 8, the sensing unit 52 also includes apair of laterally spaced apart pivot pins 90 and 92 which are press-fitinto bores in the housing 56. Left and right sensing arms 94 and 96 arepivotally mounted on the corresponding pivot pins 90 and 92. A bracingbar 98 receives both pins 90 and 92 and is bolted to the housing 56 bythree bolts 100. Pivot pin 90 divides left arm 94 into a longer armportion 102 and a shorter arm portion 104. Pivot pin 92 divides rightarm 96 into a longer arm portion 106 and a shorter arm portion 108.Washers 110 are placed on pin 90 on both sides of arm 94, and washers112 are placed on pin 92 on both sides of arm 96. Left short arm portion104 is coupled to an end 114 of draft bar 32 by left sensing link 116.Right short arm portion 108 is coupled to an end 118 of draft bar 34 byright sensing link 120. The longer second portions 102, 106 of the arms94, 96 engage the ends of a linear displacement transducer 119. Thelonger second portions 102, 106 of the arms 94, 96 move away from eachother and disengage from the transducer 119 when draft force exceeds athreshold.

A resilient member 121 includes a pair of coil springs and is coupled tothe longer portions 102, 106 of the first and second arms 94, 96, and isbiased to urge the longer portions 102, 106 towards each other. A stopmember 123 positioned between the longer portions 102, 106 and isengagable with the longer portions 102, 106 to limit movement of thelonger portions 102, 106 towards each other.

The sensing links 116 and 120 extend transversely with respect to thefore-and-aft direction. The linear displacement transducer 119 has afirst end coupled to longer arm portion 102 and a second end coupled tolonger arm portion 106. Transducer 119 generates an electrical draftforce signal, since the deflection of the sensing arms 94 and 96 is afunction of the draft force applied to draft ears 12 and 14. Thus, thesensing unit 52 mechanically sums deflection of the second portions 44,46 of the draft bars 32, 34 and applies the summed deflection to thetransducer 119. The second portions 44, 46 move away from each other anddisengage from the sensing links 116, 120 when draft force is less thana threshold.

Referring now to FIG. 8, right sensing link 120 includes a stainlesssteel rod 122 which has a forked end 124 which is pivotally coupled toright short arm portion 108 by a pivot pin 126. Rod 122 includes athreaded central axial bore 126 which receives a threaded bolt 128 whichhas a head 130 which engages the end 118 of draft bar 34. A backup nut132 is threaded onto bolt 128 to hold bolt 128 in a proper positionrelative to rod 122. A hollow bronze bushing 134 is received in housingbore 76 and the rod 122 is slidably received by the bushing 134. Abellows seal 136 has an inner end attached to the bushing 134 and anouter end attached to an outer end of the rod 122. A pair of O-ringseals 136 are mounted in grooves in the outer surface of rod 122 andprovide a seal between the rod 122 and the bushing 134. Sensing link 116is a mirror image of link 120.

Viewing FIG. 6, an increase in substantially rearwardly directed draftforces will bend the draft ears 12 and 14 and cause the ends 114 and 118of the draft bars 32 and 34 to move inwardly and towards each other.This causes the longer portions 102 and 106 of arms 94 and 96 to moveaway from each other and increase the length of the transducer 119. Infact, if the draft forces exceed a high threshold, the longer portions102 and 106 will disengage from the transducer 119 and thereby protectthe transducer 119 from draft force overloads.

Also viewing FIG. 6, a decrease in draft forces (or a forwardly directeddraft force) will cause the ends 114 and 118 of the draft bars 32 and 34to move outwardly and away from each other. This causes the longerportions 102 and 106 of arms 94 and 96 to move towards each other anddecrease the length of the transducer 119. In fact, if the draft forcesare less than a low threshold, the ends 114 and 118 will disengage thebolt heads 130 of the sensor links 116 and 120, and thereby protect thetransducer 119 from draft force underloads.

The result is a draft sensing system which is compact and which has ahousing which protects critical parts from dirt accumulation.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such illustration and description isto be considered as exemplary and not restrictive in character, it beingunderstood that illustrative embodiments have been shown and describedand that all changes and modifications that come within the spirit ofthe disclosure are desired to be protected. It will be noted thatalternative embodiments of the present disclosure may not include all ofthe features described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations that incorporate one or more ofthe features of the present disclosure and fall within the spirit andscope of the present invention as defined by the appended claims.

What is claimed is:
 1. A draft sensing mechanism comprising: a hitchframe adapted to be attached to a frame of a vehicle: left and rightlink supports each link support coupling a corresponding left and rightdraft link to a corresponding left and right side of the hitch frame;left and right draft bars, each draft bar having a first portionattached to a corresponding one of the link supports, each draft barhaving a second portion positioned rearwardly and inwardly with respectto its first portion, draft forces applied by the draft links to thelink supports deflecting the second portions of the draft bars; a draftforce transducer generating a draft force signal in response todeflection thereof; and a linkage unit which deflects the transducer inresponse to deflection of the second portions of the draft bars.
 2. Thedraft sensing mechanism of claim 1, wherein: the linkage unit iscontained in a housing which is fixed to an underside of the hitchframe.
 3. The draft sensing mechanism of claim 1, wherein: each draftbar is L-shaped and its first portion extends substantiallyperpendicularly with respect to its second portion.
 4. The draft sensingmechanism of claim 3, wherein: each first portion extends laterallyoutwardly from a forward end of the second portion.
 5. The draft sensingmechanism of claim 3, wherein: each second portion extends rearwardlyfrom an inner end of the first portion.
 6. The draft sensing mechanismof claim 3, wherein: each second portion is positioned between acorresponding link support and the hitch frame.
 7. The draft sensingmechanism of claim 1, wherein: each draft bar first portion is attachedto a forward facing surface of a corresponding one of the link supports.8. The draft sensing mechanism of claim 1, wherein: the hitch frameforms a downwardly opening pocket; and the transducer and linkage unitare received by said pocket.
 9. The draft sensing mechanism of claim 1,wherein: the linkage unit is positioned between the draft bars.
 10. Thedraft sensing mechanism of claim 1, wherein: the linkage unit ispositioned between the draft bars and between a drawbar and the hitchframe.
 11. A draft sensing mechanism comprising: a hitch frame adaptedto be attached to a frame of a vehicle: left and right link supportseach link support coupling a corresponding left and right draft link toa corresponding left and right side of the hitch frame; left and rightdraft bars, each draft bar having a first portion attached to a frontsurface of a corresponding one of the link supports, each draft barhaving a second portion positioned rearwardly and inwardly with respectto its first portion, draft forces applied by the draft links to thelink supports deflecting the second portions of the draft bars; a draftforce transducer generating a draft force signal in response todeflection thereof; and a linkage unit which deflects the transducer inresponse to deflection of the second portions of the draft bars.